1. Field of the Invention
The invention relates to an image forming apparatus and an image forming method capable of recording image information and additional information added separately from the image information to a photographic printing medium, particularly to an image forming apparatus and an image forming method capable of recording additional information in an invisible manner under normal conditions without compromising the photographic printing quality of image information.
2. Description of the Related Art
As an image forming apparatus, there has been known a thermal printer that uses a thermal head that faces a platen. In such a thermal printer, a plurality of heat-generating elements (for example, heat-generating resisters) linearly arranged on the thermal head are selectively energized according to grayscale levels, and heat energy generated during this process is used to record image information.
That is, after a photographic printing medium and an ink ribbon are transported to the platen, the thermal head is lowered so that the photographic printing medium and the ink ribbon are sandwiched between the platen and the thermal head. Then, the heat-generating elements on the thermal head are selectively energized and the ink on the ink ribbon is transferred onto the photographic printing medium so as to record image information.
The ink ribbon used in such a thermal printer is wound over a supply reel and a take-up reel in an ink cassette and configured such that a plurality of different color inks (for example, inks of yellow (Y), magenta (M) and cyan (C)) and a transparent laminate ink (L) are sequentially and repeatedly arranged on a base film in the direction perpendicular to the unreeling direction of the ink ribbon.
The color inks (Y, M and C) are sequentially applied to the photographic printing medium based on the image information so that the image information is recorded. On the other hand, the laminate ink (L) is provided to protect the image recorded with the color inks (Y, M and C) from ultraviolet light and includes an ultraviolet light absorber. Therefore, the laminate ink (L) is laminated over the area of the photographic printing medium where the image information has been recorded.
As thermal printers are finding application in various fields, in addition to image information, additional information is recorded in quite a few cases. That is, in recent years, thermal printers have been used in various fields, for example, for amusement and medical purposes. Their applications are not limited to simply printing for personal enjoyment but are as diverse as ID cards, passports and the like. Accordingly, in addition to image information, additional information associated or accompanied with the image information is recorded for numerous purposes, such as for preventing counterfeit and tampering, and recording photographing information, such as date and time as well as imaging conditions.
There has been proposed an image forming apparatus capable of recording image information and additional information added separately from the image information to a photographic printing medium. That is, there is disclosed an image forming method for, for example, manufacturing an ID card that provides an anti-counterfeit effect by laminating transparent plastic members, each having different thickness for each pixel, on a recorded image previously formed by using a dye (see U.S. Pat. No. 5,990,918, for example).
There has also been disclosed an image forming apparatus that provides a film-like sheet (laminate film) coating on the image information recorded surface of a photographic printing medium so as to provide difference in surface glossiness, thereby rendering additional information, such as photographing information including date and time as well as imaging conditions, invisible when viewed from the front of the photographic printing medium but visible only when viewed from an oblique direction (see JP-A-2002-240402, for example).